Fischer-Tropsch synthesis is known to yield a broad mixture of products including primarily paraffins, and some olefins. The individual compounds of such mixture can contain up to about 200 carbons, the number of carbons between about 20 and about 150, with average number about 60 being typical. Certain quantities of oxygenated products and trace amounts of sulfur- or nitrogen containing products or aromatic compounds can be also present.
Some Fischer-Tropsch processes yield mixtures enriched with C5-C30 alkanes and also containing a significant quantity of olefins and oxygenated compounds such as alcohols or acids. Such mixtures are known as “light Fischer-Tropsch liquids” or “LFTL.” Light Fischer-Tropsch liquids are frequently used as a raw material for obtaining various petrochemical products, such as, e.g., petroleum distillates, or diesel fuels, among others.
To make LFTL useful and suitable as blending stock for diesel fuel, olefins and oxygenated compounds contained therein are removed, typically by the saturation of olefins and by conversion of oxygenated compounds into water via hydrogenation also known as hydrotreating, which involves the processes of hydrogenation of LFTL in the presence of hydrogen and a catalyst.
Despite its many advantages, hydrotreating of LFTL is characterized by a number of drawbacks and deficiencies. For example, the process usually requires using very high pressures and temperatures. In addition, while traditional hydrotreating does allow for removal of olefins and oxygenated compounds, the final product often has a cloud point that is too high, limiting the amount of the product that can be blended into diesel fuels.
To avoid or lessen the effects of the above-mentioned deficiencies, as well as for the purposes of improvement of the overall process efficiency, better processes are needed to be used with light Fischer-Tropsch liquids.